A numerical control apparatus is an apparatus for performing numerical control processing based on a machining program commanded from a paper tape etc., and driving a machine tool by the processing result and subjecting a work to the machining as commanded.
FIG. 10 is a main block diagram showing a conventional numerical control apparatus.
In the drawing, numeral 101 shows a numerical control apparatus, and comprises an analysis processing part 103, an interpolation processing part 104, a machine control signal processing part 106, a PLC circuit 105, an NC spindle control part 180, a main spindle control part 110, a data input/output circuit 120, memory 107, a parameter setting part 108 and a screen processing part 109. Also, the numerical control apparatus 101 is coupled to a servo driving apparatus 201 through the data input/output circuit 120 to drive an NC spindle 204. Also, the numerical control apparatus 101 is coupled to a main spindle driving apparatus 301 through the data input/output circuit 120 to drive a main spindle 304.
Numeral 102 is a machining program, and the machining program 102 read from a tape reader etc., is stored in the memory 107.
As shown in FIG. 12, in this machining program 102, three kinds ($1: system 1, $2: system 2, $3: system 3) are managed as one machining program. This is generally referred to as a multiple-system machining program, and the present numerical control apparatus 101 can analyze and execute the multiple system machining program in parallel.
When the multiple-system machining program is applied to a configuration of a machine tool, for example, it becomes as shown in FIG. 11.
That is, the present machine tool is configured by a first tool rest, a second tool rest and a third tool rest. A front workpiece is machined by a tool mounted in the first tool rest, a tool mounted in the second tool rest, and a tool mounted in the third tool rest, respectively. Also, an opposed workpiece is machined by the tool mounted in the second tool rest. Here, a machining program of the system 1 is allocated to the first tool rest, a machining program of the system 2 is allocated to the second tool rest and a machining program of the system 3 is allocated to the third tool rest.
Next, blocks of the machining program 102 of each the system are read out of the memory 107 one by one and are respectively analyzed by the analysis processing part 103. A code analyzed every one block is passed to the interpolation processing part 104, and according to a command, interpolation control, main spindle control, auxiliary function control, etc., every one block are performed. The NC spindle control part 180 performs control for positioning or interpolation feeding, etc., according to interpolation data with respect to an NC spindle. The main spindle control part 110 performs control for performing actions such as rotation of a main spindle by a commanded number of revolutions, a stop, an orientation action of the main spindle with respect to a main spindle commanded.
The servo driving apparatus 201 is coupled to a servo motor 202 and drives the NC spindle 204 through gears, ball screws, etc., by position control by means of position feedback from a detector 205.
The main spindle driving apparatus 301 is coupled to a main spindle motor 302 through gears etc., and drives the main spindle 304. A detector 305 is mounted in the main spindle 304 and the main spindle driving apparatus 301 can control an orientation action of the main spindle motor 302 by position data inputted from the detector.
By the way, the numerical control apparatus preferably has a program resumption function (a function of halting the machining and evacuating and replacing a tool and then returning the evacuated tool and then resuming the machining when the tool breaks or wears during the machining).
In a numerical control apparatus in correspondence with a single system (only a system 1), the program resumption function has been present conventionally, but in a machine tool equipped with a numerical control apparatus in correspondence with multiple systems, generally, the number of control spindles is very large and it is very difficult to restore a synchronous relation between the systems and resume machining, so that the program resumption function for restoring the synchronous relation between the systems and resuming the machining has not been present yet in the numerical control apparatus in correspondence with multiple systems described above.